This invention relates to fluid diffusers, and particularly to an improved diffuser that is useful for introducing bubbles of air into wastewater to be treated.
In the aeration treatment of wastewater, it is common to introduce the air through a series of submerged diffusers mounted at spaced positions along the length of a manifold pipe. The diffusers have apertures through which the air can escape, preferably as small bubbles. A common type of diffuser uses a rubber or rubber-like flexible diaphragm working against a flat, rigid disc. When air is not being admitted to the diffuser, the flexible diaphragm seats against the hard disc under the pressure of the water and seals the air openings thereby functioning as a check valve. When air is admitted under pressure, the flexible diaphragm moves away from the disc and opens the apertures to allow the air to escape.
One form of flexible diaphragm diffuser is disclosed in U.S. Pat. No. 3,525,436 issued Aug. 25, 1970 to D. J. Reckers for "Sewage Treatment Plant." In the diffuser of that patent, the rigid disc has a series of holes located inwardly of its perimeter. The flexible diaphragm overlays the top surface of the disc and is joined to the perimeter of the disc by a clamp. When air is introduced under pressure sure through a central opening in the disc, the diaphragm is unseated and air can pass between the diaphragm and the top surface of the disc and out the bottom of the disc through the holes.
Another form of diaphragm diffuser traps the diaphragm between the top surface of the disc and an upper retaining ring. When air under pressure is admitted through a central disc opening, the diaphragm moves off of the top of the disc and air can escape radially outwardly between the disc and the diaphragm.
In contrast to the above forms that use clamps or retainer rings to hold the diaphram to the disc, another approach is characterized by relying on the resiliency of the diaphragm to hold it to the rigid disc. In this approach, the rigid disc typically has a scalloped perimeter that is grasped by a rim of the diaphragm. In one version, holes are provided in the diaphragm and the holes are closed until the diaphragm is moved away from the disc when air is admitted through a central opening in the disc. Another version of this approach is described in the copending application Ser. No. 655,890, now U.S. Pat. No. 4,597,530 of Paul R. Goudy, et al. for "Fluid Diffuser", filed Aug. 28, 1984 and assigned to the assignee of this application. The diffuser of that application has a diaphragm that is uninterrupted by holes and the air passages are instead provided at the valleys of the scalloped perimeter which are not covered by the diaphragm.
All such air diffusers encounter the problem of the build-up of deposits in the air openings, particularly when hard water is treated. The resulting calcium deposits can partially close the air passages if the operation of the diffuser does not tend to cause the deposits to be physically broken up. The resulting increase in air pressure working against the diaphragm can cause the diaphragm to be blown loose of the disc in those diffusers that do not use clamps or retaining rings. The use of a softer, more flexible material for the diaphragm tends to break-up and dislodge deposits because of the greater flexing of the diaphragm during use. The softer material also provides better sealing against the disc when the diaphragm is functioning as a check valve. However, the use of softer material increases the tendency to blow the diaphragm loose from the scalloped edges of the rigid disc.
A diffuser in accordance with the present invention uses the resiliency of the diaphragm to hold it in place on the rigid disc, but because of the manner of mounting the diaphragm, a soft, flexible elastomer can be used without danger of blowing-off the diaphragm even under extreme fluid pressure overloads. The diffuser also insures the formation of small, discrete bubbles or drops of the fluid being diffused. Although the diffuser is particularly useful in diffusing air or other gas into a liquid, it is also useful for introducing one liquid into another. Accordingly, the diffuser is capable of handling fluids of all types, both liquids and gasses.